Cell temperature regulation

ABSTRACT

An energy storage system includes an energy storage component. It further includes heat generating electronics. It further includes a fluid circulator that transfers fluid between the energy storage component and the heat generating electronics. The circulator is controlled to alternatively transfer fluid from the battery to the heat generating electronics or from the heat generating electronics to the energy storage component based at least in part on a thermal state of the energy storage system.

CROSS REFERENCE TO OTHER APPLICATIONS

This application claims priority to U.S. Provisional Patent ApplicationNo. 63/245,004 entitled MODULAR ENERGY STORAGE SYSTEM filed Sep. 16,2021 which is incorporated herein by reference for all purposes.

BACKGROUND OF THE INVENTION

Energy storage systems are complex, where various considerations must betaken into account when designing an energy storage system, from safetyconsiderations due to the risk of fire, to on-site installation ofbattery systems. Thus, the design of energy storage systems can bechallenging.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the invention are disclosed in the followingdetailed description and the accompanying drawings.

FIG. 1 illustrates an embodiment of a power system.

FIG. 2 illustrates an embodiment of a battery block.

FIG. 3 illustrates an embodiment of an electrical layout of a batteryblock.

FIG. 4A illustrates an embodiment of a battery block.

FIG. 4B illustrates an embodiment of a battery block.

FIG. 4C illustrates an embodiment of air flow in a battery block tofacilitate cooling.

FIG. 5 illustrates an embodiment of a cooling structure of a batteryblock.

FIG. 6 illustrates an embodiment of a battery block.

FIG. 7 illustrates an embodiment of a battery module.

FIG. 8A illustrates an embodiment of a top-down view of a batterymodule.

FIG. 8B illustrates an embodiment of a cross-section view of a batterymodule.

FIG. 8C illustrates an embodiment of a busbar for connecting batterysub-modules.

FIG. 9A illustrates an embodiment of a sensor interface of a batterymodule.

FIG. 9B illustrates an embodiment of sensor wiring of a battery module.

FIG. 10A illustrates an embodiment of a battery module.

FIG. 10B illustrates an embodiment of thermally absorptive pouchesbetween battery modules.

FIG. 10C illustrates an embodiment of a central rib of a battery module.

FIG. 11A illustrates an embodiment of exhaust ports of a battery module.

FIG. 11B illustrates an embodiment of an exhaust port of a batterymodule.

FIG. 12A illustrates an embodiment of a battery block.

FIG. 12B illustrates an embodiment of a battery block.

FIG. 13 illustrates an embodiment of a power system.

FIG. 14 illustrates an embodiment of bi-directional fan control andlogic.

FIG. 15A illustrates an embodiment of an open-air loop operation modefor cooling.

FIG. 15B illustrates an embodiment of an open-air loop operation modefor heating.

FIG. 15C illustrates an embodiment of a closed-air loop operation mode.

FIG. 16A illustrates an embodiment of an open-loop operation mode.

FIG. 16B illustrates an embodiment of a closed-loop operation mode.

DETAILED DESCRIPTION

The invention can be implemented in numerous ways, including as aprocess; an apparatus; a system; a composition of matter; a computerprogram product embodied on a computer readable storage medium; and/or aprocessor, such as a processor configured to execute instructions storedon and/or provided by a memory coupled to the processor. In thisspecification, these implementations, or any other form that theinvention may take, may be referred to as techniques. In general, theorder of the steps of disclosed processes may be altered within thescope of the invention. Unless stated otherwise, a component such as aprocessor or a memory described as being configured to perform a taskmay be implemented as a general component that is temporarily configuredto perform the task at a given time or a specific component that ismanufactured to perform the task. As used herein, the term ‘processor’refers to one or more devices, circuits, and/or processing coresconfigured to process data, such as computer program instructions.

A detailed description of one or more embodiments of the invention isprovided below along with accompanying figures that illustrate theprinciples of the invention. The invention is described in connectionwith such embodiments, but the invention is not limited to anyembodiment. The scope of the invention is limited only by the claims andthe invention encompasses numerous alternatives, modifications andequivalents. Numerous specific details are set forth in the followingdescription in order to provide a thorough understanding of theinvention. These details are provided for the purpose of example and theinvention may be practiced according to the claims without some or allof these specific details. For the purpose of clarity, technicalmaterial that is known in the technical fields related to the inventionhas not been described in detail so that the invention is notunnecessarily obscured.

FIG. 1 illustrates an embodiment of a power system. In this example, thepower system 100 includes an inverter (102). The power system alsoincludes an energy storage system (ESS) 104. In this example, ESS 104 isa battery storage system. In other embodiments, the energy storagesystem is implemented using other forms of energy storage, such as fuelcells. In some embodiments, the energy storage system is a modularsystem that includes a stack of battery blocks (also referred to hereinas battery assemblies) that are connected to inverter 102. Each batteryblock further includes a stack of battery modules that are connectedtogether. Further details regarding a modular battery storage system,such as embodiments of electrical and thermal operation of the modularbattery storage system are described below. An example of a power systemincluding a stack of battery blocks connected to an inverter is shown inFIG. 13 .

Battery Block

FIG. 2 illustrates an embodiment of a battery block. In someembodiments, battery block 200 is an example of a battery block in astack of battery blocks included in an energy storage system such as ESS104 of FIG. 1 .

In this example, the battery block includes a stack of battery modules,such as battery module 202. The battery modules are connected together.As will be described in further detail below, each battery moduleincludes a set of energy storage components such as battery cells (e.g.,as battery cell pouches), fuel cells, etc. For illustrative purposes,embodiments of battery modules including battery cells are describedbelow. While a battery block including six battery modules is describedherein for illustrative purposes, a battery block may include any numberof battery modules, as appropriate. Further details regarding batterymodules are described below.

When viewing the battery block of FIG. 2 , the left side 204 of thebattery block is referred to herein as the “front” or “terminal end” ofthe battery block, and houses various electrical components of thebattery block, as will be described in further detail below. The rightside 206 of the battery block is referred to herein as the “rear” or“exhaust end” of the battery block.

The following are embodiments of the electrical and thermal design of abattery block.

Battery Block Electrical Design

FIG. 3 illustrates an embodiment of an electrical layout of a batteryblock. In this example, a perspective view of portion 204 of batteryblock 200 of FIG. 2 is shown. As described above, in some embodiments, abattery block includes a stack of connected battery modules.

As shown in this example, and as will be described in further detailbelow, each module includes two electrical terminals/electrodes. Bothelectrodes are on the same face of the module. In some embodiments, andas will be described in further detail below, the cells within a moduleare connected in series in a manner to form a U-shape so that the anodeand cathode can be on the same side of the module (rather than, forexample, on opposing sides). Electrodes 302 and 304 are examples of theelectrodes for module 202.

In this example, the battery modules are stacked in series by usings-shaped busbars (module-to-module busbars) such as s-shaped busbar 306.Here, the busbar between one module to the next connects an anode of onemodule to the cathode of another module, or the cathode of one module tothe anode of another module. An overall stack/block busbar 308 thenbrings the top module back down to give the full stack voltage into theDC-DC converter 310.

The electrical series connection of the battery modules as shown in theexample of FIG. 3 allows the addition of the voltages of the individualbattery modules. As one example, each module operates at 8.4V. Here, thebattery block includes six modules/cans. This results in the batteryblock operating at a voltage of approximately 50 volts (8.4V×6).

As described above, the stack of series-connected modules are connected,via 302 to a DC-DC converter 310, which then feeds the stacked voltagesup to an inverter (e.g., inverter 102 of FIG. 1 ). In some embodiments,the DC-DC converter boosts the voltage, for example, from 50V to 200V.The DC-DC converter may also be a buck converter that reduces the inputvoltage, or be a buck-boost converter that operates in either buck orboost mode.

Shown in this example portion of the battery block is a portion orsegment 312 of a wiring harness that plugs into the DC-DC converter. Asdescribed above, a battery storage system may include a stack of batteryblocks. For example, each battery block may have a capacity of 5 kWh,where a stack of three battery blocks results in a battery storagesystem with a capacity of 15 kWh.

In this example, plug 312 and associated wiring is a portion or segmentof a wiring harness that connects one battery block to another,ultimately connecting to the inverter. In some embodiments, the wiringharness carries both power and signal from the blocks to the inverter.For example, a portion of the wires of the harness are used forcommunication among the inverter and battery modules. Another set ofwires are used to carry high voltage output from the DC-DC converters.In some embodiments, the wiring harness is touch-safe. In someembodiments, the harness is adjustable, and segments can be added orremoved depending on the number of battery blocks to be connected (e.g.,the harness is a segment-style harness that is extendable to accommodatemore blocks that are added). In other embodiments, each configuration ofbattery blocks has its own corresponding one-piece harness. That is,there is one harness for each setup configuration (e.g., one harness fora three block system, another harness for a six block system, etc.).Further details regarding the wiring harness are described below.

Battery Block Thermal Design

The battery block is designed to provide thermal management in variousmodes, such as normal operation or in the event of thermal events.

Normal Operation Thermal Behavior

The following are examples and embodiments of cooling and airflow of thebattery stack during normal operation

FIGS. 4A and 4B illustrate embodiments of a battery block. As shown inthis example, during normal operation, air is pulled into a duct orchannel formed by the long sides of the battery modules in the batteryblock and an outer cosmetic shroud 402 covering the battery modules thatincludes vents or ducts. The air flow is caused by and directed throughthe channel by fan 404. While a single fan is shown in this example forillustrative purposes, in other embodiments, multiple smaller fans mayalso be used. As one example, six smaller fans may be used, where thereis one fan for each module in the battery block. For example, multiplesmaller fans connected in parallel or in series may be used. While a fanis shown in this example for illustrative purposes, any other air/fluidcirculator may be used as applicable.

As shown in this example, the shroud covers the battery modules, butdoes not seal the modules. The shroud has ducts to allow air to come inand out of the battery stack. The air that is drawn through the channelalong the sides of the battery modules carries away heat generated bythe battery cells, cooling the modules down. The heated air is thenfurther cooled using, for example, a heat sink such as heat sink 408 ofportion 406 of the battery stack.

FIG. 4C illustrate an embodiment of air flow in a battery block tofacilitate cooling. In this example, a top down view of the batteryblock of FIG. 4B is shown. In this example, the fan 404 (under amanifold/duct 414 in the example of FIG. 4C) draws in air from a port onthe right side of the cover 402 over the battery block (where the porton the right side is the inlet for this direction of airflow). The airthen splits around the battery modules, where a portion of the air willgo around the back side (410) of the module (on the side near the wall),where the other half of the air will flow around the front side (412) ofthe module. This flowing of air cools the six battery modules in thebattery block. Once past the battery modules, the split air flows willboth then flow into a duct (414) and merge when going through the fan.The duct acts as a manifold in which the six air channels on each sideof the battery block flow into the fluid volume at the location of thefan. That is, the manifold aggregates the air branches and directs themerged air through the fan, which is the air driver/mover. The mergedair is then pushed by the fan over the heat sink, where in someembodiments, the power electronics are mounted on the heat sink, therebycooling the power electronics. The air is then split around the heatsink, before it merges again and exits out of the port/opening on theleft side of the battery block (exhaust in this direction of airflow).In this example, although the ambient air may be warmed to some extentby the battery cells, because the cells operate with high efficiency,the cells generate little waste heat during normal operations. Thus, theair, even after passing over the battery modules, is still usable tocool the power electronics.

As will be described in further detail below, in some embodiments, thefan is bi-directional, and the direction of the fan may be reversed tofacilitate warming of the battery cells, as well as temperatureregulation.

FIG. 5 illustrates an embodiment of a cooling structure of a batteryblock. In this example, a profile view of portion 406 of the batteryblock of FIG. 4B is shown. In this example, the fan 404 draws air fromthe right side of the modules of the battery block (as oriented in theexamples of FIGS. 4A and 4B), where it is fed into ductwork and into thefan and then out through heatsink 502 (an example of heat sink 408 ofFIG. 4B), which in some embodiments also cools the DC-DC converter 310.In this example, the heatsink is implemented using pin fins. Other typesof heat sinks may be used, as appropriate.

Thus, as shown in this example, in normal operation, ambient air is runacross the long sides of the modules to cool the modules down. As willbe described in further detail below, the long sides of the modules maybe made using a thermally conductive material such as coated steel toallow efficient transfer of heat.

Thermal Event Behavior

Thermal runaway events may occur in battery cells, where a battery cellcatches fire. As will be described in further detail below, in someembodiments, each battery module is designed to mitigate the impact ofthermal runaway events, for example, by including vents that are used toexhaust gases from within the module in case of thermal runaway.Described herein are techniques for exhausting such gases in a mannerthat is controlled and also allows for the exhaust gases to be cooled.This prevents the exhaust gases from causing other objects near thebattery stack/storage system to ignite.

FIG. 6 illustrates an embodiment of a battery block. As shown in thisexample, the exhaust gases from the battery modules are vented outthrough exhaust ports at 602. Further details regarding the exhaustports of the battery modules are described below. In this example,outside of the exhaust ports of the individual modules, a heat exchanger604 (also referred to herein as a heat diffuser) is shown. In someembodiments, the heat exchanger takes the hot air exhausted out of themodules and filters it through a series of perforated metal plates. Inthis way, the heat from the exhausted gas is dumped into the metalbefore it exits. The passage of the gas through the various layers ofmetal causes the exhaust gases to be cooled down by the time the gasleaves this exhaust diffuser (e.g., to be below the ignition temperatureof cheesecloth used for a cheesecloth test). As shown in this example,the exhaust diffuser is shared by the modules (where the modules allfeed into the same shared exhaust diffuser). In this way, the mass ofthe entire heat exchange system can be shared amongst the modules.

Battery Module

FIG. 7 illustrates an embodiment of a battery module. Battery module 700is an example of module 202 of FIG. 2 . In some embodiments, the batterymodule (also referred to herein as a “can”) is a sealed enclosure thatincludes battery cells. For example, the modules are sealed by a shellthat is IP67 sealed. The shell (also referred to herein as a “can”) isalso made of a thermally conductive material to facilitate thermalmanagement, as will be described in further detail below. A cutout viewof a battery module is shown in the example of FIG. 7 . In this exampleorientation of a battery module shown in FIG. 7 , a “side” view of theinternal structure of a battery module is shown. The portion 702 of thebattery module is referred to herein as the “front” or “terminal side”of the battery module. The front of the battery module includesterminals or electrodes for connecting multiple modules together to forma series connection of modules in a battery block, as described above.The terminal side of the battery module includes various electronicssuch as sensor ports as well. Portion 704 of the battery module isreferred to herein as the “back” or “rear” or “exhaust side” of thebattery module and includes venting for allowing gases to be expelled,as will be described in further detail below. The portion 706 of thebattery module is referred to as the “top” of the module, and theportion 708 of the battery module is referred to as the “bottom” of thebattery module.

The following are embodiments of examples of the electrical and thermaldesign of a battery module.

Battery Module Electrical Design

FIGS. 8A and 8B illustrate embodiments of a battery module. In someembodiments, FIGS. 8A and 8B illustrate different perspective views ofbattery module 700 of FIG. 7 .

FIG. 8A illustrates an embodiment of a top-down view of a batterymodule. As shown in this example, the battery module is oriented suchthat the front terminal-side of the battery module 802 is at the bottomof FIG. 8A. As shown in this example, the battery module is divided intotwo compartments or sub-modules, 804 and 806. The compartments areseparated by a central partition or rib 808. In some embodiments, eachcompartment is separately sealed from the other. Within each compartmentis one or more battery cells. As one example, the battery cells arelithium-ion cells. In some embodiments, the battery cells areimplemented using pouches. In this example, a battery module includesfour battery pouches in total, with two battery cells in eachcompartment. In some embodiments, a battery pouch is substantiallyplanar, and the two pouches within a compartment are stacked on top ofeach other.

FIG. 8B illustrates an embodiment of a cross-section view of a batterymodule. In this example, the internal structure of a battery module isshown from the front of the battery module. The central rib of thebattery module is shown at 808. The compartments/sub-modules of thebattery module are shown at 804 and 806. As described above, in thisexample, the battery module includes four battery cell pouches, with twopouches in each compartment. In this example, compartment 804 includesbattery cells 810 and 812. Compartment 806 includes battery cells 814and 816. As shown in this example, each cell is substantially planar.Here, there are two cells stacked on top of each other in eachsub-module compartment of the module.

In this example, the two battery cell pouches in a compartment areconnected in series. As one example, the voltage on eachsub-module/compartment has an operating voltage of 4.2V (at top ofcharge). In some embodiments, the sub-modules of the two compartmentsare further connected in series, resulting in an overall voltage of 8.4Vfor the entire battery module 700. For example, a busbar is used toconnect the battery cells of the two compartments in series, as will bedescribed in conjunction with FIG. 8C.

FIG. 8C illustrates an embodiment of a busbar for connecting batterysub-modules. FIG. 8C illustrates an embodiment of a cutaway of the rearof the battery module. As shown in the example of FIG. 8C, a busbar 818connects the electrode of one battery sub-module of a compartment to anelectrode of the other battery sub-module in the other compartment,connecting the sub-modules in series. As shown in this example, thecomponents of the module are arranged such that they form a “U” shape sothat both electrodes of the battery module are on the same face (e.g.,terminal-side) of the battery module.

Sensor Layout

The battery module further includes various sensors for measuring thehealth of the battery module and the battery cells. Further detailsregarding the arrangement of sensors in a battery module are describedbelow.

FIG. 9A illustrates an embodiment of a sensor interface of a batterymodule. In this example, a portion of the front or terminal-side of abattery module is shown. A sensor port or interface is shown at 902. Insome embodiments, port 902 provides connectivity to voltage andtemperature sensing locations. Having such a port is an improvement overexisting sensing solutions, which typically involve running wires orring terminals to the electrodes of the battery module to collectvoltage measurement values. Here, this is done internally, for example,using a wiring harness internal to the module.

FIG. 9B illustrates an embodiment of sensor wiring of a battery module.In this example, a top-down perspective showing a portion of theterminal-side of the battery module is shown. As shown in this example,the internal wiring harness includes voltage and temperature sensorconnection points such as sensor connection point 904 that is connectedto the port 902.

In some embodiments, this wiring and sensor arrangement providesimproved ease of manufacturing, and is also less expensive to produce.Here, instead of running individual ring terminals to each of theterminals in addition to including external temperature sensors, thereis one connector to plug into to obtain all of the data needed toevaluate cell health. The use of such connectors for sensor health ismore automatable than handling ring terminals, and does not requireattachment of wires in-situ during the assembly process using, forexample, ultrasonic welding. Here, the sensors are easily connected toby simply plugging into the provided port. This simplifies assembly atmanufacturing time.

In some embodiments, the cell health information is then passed to theexternal wiring harness described above (that connects to the batteryblocks and the inverter), where the information is passed to a computingnode for processing and analysis. For example, the computing device is apart of the inverter.

Battery Module Thermal Design

As will be described in further detail below, the design of the batterymodules described herein reduces the impact of thermal runaway events.This includes two parts. First, when one cell goes into runaway, thethermal design of the battery module minimizes propagation of therunaway event to as few other cells as possible. As will be described infurther detail below, the design of the module provides various layersand barriers to limit the effect of thermal runaway events. Second, thegases are exhausted and cooled in such a manner that the exited gases donot create an ignition source that could ignite objects external to thebattery module or system. As will be described in further detail below,the thermal design of the modules includes venting and exhaust portsthat facilitate cooling of the gasses.

Preventing Propagation of Thermal Events

FIG. 10A illustrates an embodiment of a battery module. In this example,FIG. 10A illustrates a cutaway cross-section view of the battery modulefrom the front of the battery module.

Insulation

As described above in conjunction with FIG. 8B, the battery module issplit into two compartments, where each sub-module includes two batterypouches. In some embodiments, the battery module includes layers ofinsulation/foam at the top and bottom of the compartments to providethermal management. Examples of thermal insulation are shown at 1002,1004, 1006, and 1008.

Thermally Absorptive Pouch

In various embodiments, the battery assembly includes thermal managementsolutions for inter-module thermal management. In various embodiments,the thermal management solutions include active and/or passive thermalmanagement solutions. Examples of passive thermal management solutionsinclude insulating materials, thermally absorptive materials, etc. Insome embodiments, the top of the battery module includes a geometry suchas a depression or indentation for locating or holding a thermalmanagement solution such as a pouch of thermally absorptive material.The pouch of thermally absorptive material is used to absorb heat from arunaway event in one battery module and prevent that heat frompropagating to the next battery module that is stacked above.

FIG. 10B illustrates an embodiment of thermally absorptive pouchesbetween battery modules. In this example, a stack of battery modules ina battery block is shown, where one battery module is stacked on top ofanother battery module. As shown in this example, pouches of thermallyabsorptive material 1010-1020 are placed on the top of each batterymodule, such that when one battery module is stacked on top of another,the pouch of thermally absorptive material is sandwiched between the twobattery modules. In this way, propagation of heat from the module belowto the module above is mitigated. Thus, top-to-bottom propagation ofheat is limited.

In some embodiments, the thermally absorptive material in a pouch is agel. The thermally absorptive material may also include a phase changematerial. In some embodiments, the thermally absorptive pouch includes aliquid such as water or a liquid that vaporizes or boils off. Asdescribed above, the thermally absorptive pouch provides a form ofinsulation between battery modules and controls or mitigates the impactof thermal events. The thermally absorptive pouch may also be used forcooling during normal operation.

The insulation and thermally absorptive pouches described herein limittop-to-bottom propagation of a runaway event through the assortment ofbarrier layers described above. For example, when modules are stacked,there are multiple layers between the battery pouches of one module andthe battery pouches of the adjacent module. These layers include a toplayer of insulating foam of the below module, a layer of steel (the“skin” or outer shell of the module), the pouch of thermally absorptivematerial described above, the steel shell of the next adjacent module,and a bottom layer of insulating foam of the above module beforearriving at the next battery cell. These layers provide “up-to-down”propagation resistance and form a substantial barrier in preventingvertical module-to-module propagation of a thermal runaway event thatstarts in a cell of a battery module.

Central Divider Channel

As described above, a battery module includes two sealedcompartments/sub-modules that are separated by a divider or partitionsuch as a central rib. In some embodiments, the central rib is alsodesigned to limit side-to-side propagation of heat within the batterymodule.

FIG. 10C illustrates an embodiment of a central rib of a battery module.In this example, a cutaway, cross-section view of the central rib of thebattery module from the front of the battery module is shown Asdescribed above, the central rib 1022 splits the can or module into twoseparate compartments or sub-modules. In some embodiments, the centralrib is manufactured in steel.

In this example, the central rib includes a channel. The central ribfurther includes an internal piece of metal 1024 that divides thechannel into two sub-channels. The divider 1024 provides a wall betweenthe two compartments within the battery module. The internal wall limitsthe propagation of heat from one sub-module to the other sub-modulewithin the battery module. In some embodiments, the internal piece ofmetal also provides structural support.

As shown in this example, the space between the inner wall 1024 and thebattery cell pouches (e.g., cell pouches 1026 and 1028) also providesthermal insulation by providing an air gap. If a thermal event causesthe creation of a large volume of hot gas on, for example, the left sideof FIG. 10C, on the left side of the wall, there is now a large air gap,providing a “thermos” between the hot gas in the compartment on the leftand the battery cells in the compartment on the right. In someembodiments, the battery cell pouches (or whatever energy storagecomponents or devices are encapsulated in the enclosure of the module)are insulating on their own.

Further, as shown in the example of FIG. 10C, the internal wall 1024 ofthe central rib touches, at its top and bottom points (1030 and 1032,respectively), respective top and bottom layers of metal 1034 and 1036.This allows heat on the wall to be transferred to the surrounding metal,directing it away from the battery cell pouches (where, as shown in thisexample, the steel is on the outside of the foam, providing anotherbarrier between the cell pouches). In some embodiments, the metal thatthe top and bottom points of the internal wall 1024 touch are also incontact with the pouches of thermally absorptive material describedabove, further facilitating the transfer of heat away from thecompartments and to the thermally absorptive material.

Here, the channeling of gasses, the barriers such as air gaps, as wellas the transfer of heat away from battery cells provide left-to-rightpropagation resistance, making it difficult for the heat from onecompartment of the module to reach the battery cells in the othercompartment. That is, the use of the inner channel and central rib asdescribed herein limits “left-to-right” propagation, where thepropagation of a runaway event in one sub-module to the battery cells inthe other sub-module of the battery module is limited. For example,suppose that the top left pouch 1026 is the initiating pouch (that goeson fire). The runaway event will propagate to the pouch 1028 below inthe same compartment as they are touching each other. This will resultin the generation of heated gases in that compartment (e.g., due tovaporization of the electrolytes in the battery cell pouches). Theregion within the rib between the pouches and the internal wall 1024acts as an air gap, which in conjunction with the barrier provided bythe internal wall 1024 of the central rib, seals off one compartmentfrom the other, limiting the propagation of heat to the othercompartment. In some embodiments, the channel also provides an exhaustpathway that routes or channels the generated hot gas out of an exhaustport, further details of which will be described below.

Thus, using the battery module thermal design described herein,propagation of thermal runaway events is limited. This includes limitingtop-to-bottom propagation (e.g., between modules of the battery stack),and limiting left-to-right or side-to-side propagation (within themodule).

Exhausting of Heated Gases and Cooling of Exhausted Gases

As described above, the battery modules include vents for exhausting hotgases that are generated in the compartments of a module during athermal runaway event.

FIG. 11A illustrates an embodiment of exhaust ports of a battery module.In this example, a view of the rear (exhaust-side) of a battery moduleis shown. In this example, there are two vents 1102 and 1104, one foreach of the two compartments/sub-modules of the battery module. Theexhaust ports 1102 and 1104 are used to manage the gas generated by thecells during a thermal runaway event.

In this example, the vents are shown closed off by stickers. In thisway, during normal operation, the battery modules are sealed. In someembodiments, elevated pressure in the module, such as due to heatedgases caused by a thermal runaway event, causes the stickers to be blownoff, opening up the exhaust ports, allowing the gases built up insidethe compartment of the module to be exhausted out. In this way, thegases may be vented out, cooling the module.

For example, during a thermal runaway event as described above, when acell in one module ignites, the hot gases are exhausted through thecentral rib and directed to the exhaust ports/vents, where the heatedgases caused by the ignition event cause the stickers to blow off,allowing the heated gases from inside of the module to be exhausted outof the “venting side” of the module.

FIG. 11B illustrates an embodiment of an exhaust port of a batterymodule. In this example, exhaust port 1102 is shown without the coveringsticker. In this example, when an event such as a thermal runaway eventoccurs, the battery cell pouches, which are filled with electrolytes,break where they are weakest. This results in a large volume ofsuper-heated gas to be released. As described above, when a thermalrunaway event occurs, a sticker blows off to allow the gas from onecompartment of the module to vent into a shared exhaust diffuser (e.g.,diffuser 604 of FIG. 6 ). In some embodiments, the vent/exhaust port isconnected to the thermal diffuser via a sealed pipe or passage. In thisway, exhaust gases are forced to be directed through the diffuser,cooling the exhaust gases, thereby reducing the risk of ignitingsurrounding objects and increasing safety.

Battery Storage System Design for Installation

In some embodiments, the various components of the battery storagesystem described herein are designed to reduce installation complexityand improve the ease of installation.

The battery storage system described herein is scalable, where thebattery blocks described above are stackable to create battery storagesystems with varying capacities. In some embodiments, installation ofthe battery storage system includes wall mounting of the battery blocksthat make up the battery storage system, and then connecting the batteryblocks together and to the inverter. Described herein are designs thatfacilitate ease of wall mounting of the battery blocks, as well assimplified electrical connection of the battery blocks to an inverter.

Wall Mounting

FIG. 12A illustrates an embodiment of a battery block. In this example,a perspective view of a battery block is shown, where the view is fromthat of a transparent wall to which the battery block is attached.

Frames 1202 and 1204 are shown in this example. The frames run along thefronts and backs of the battery modules in the battery block. In thisexample, the frames 1202 and 1204 have hooks 1206 and 1208,respectively. In some embodiments, during installation, a bracket suchas a wall cleat is mounted to the wall. The battery block is thenmounted to the wall by hanging or hooking the hooks of the frames of thebattery block onto the wall cleat. The hooks are portions of the framesthat support the battery modules when hung on the wall. There are twoframes shown in this example. When the battery block is hung on thewall, the two frames are being supported by the hooks and the wallcleat. The frames in turn hold up the stack of battery modules in thebattery block. That is, the frames provide a mechanical base structure.Hooks are but one example of a geometry usable to attach the batteryblock. A wall bracket is but one example of a compatible wall-mountedcomponent.

In some embodiments, the battery modules are bolted to the battery blockframes, where the frames are then mounted to the wall via the hooks, asdescribed above. In this way, the battery block is mechanicallysupported. In some embodiments, the frames also have cutouts for ambientair to flow.

As shown in this example, the frames also have curved lips/flanges 1210,1212, 1214, and 1216. These lips provide mechanical structure. Further,when the block is set down, the lips provide feet for lifting the blocksoff of the ground. The curvature of the flanges also provides increasedstiffness against flexing of the frames. The flanges further distributeforce evenly across the block in the event that a battery block isaccidentally dropped. In this way, the force is not all on one corner ofthe can or module.

As shown in this example, the bottom portions 1212 and 1216 of theframes protrude. The protrusions touch against the wall to providestability and anti-rotation support. FIG. 12B illustrates an embodimentof a battery block. In this example, a “terminal-side” view of a batteryblock is shown. An example of a hook 1218 and protruding anti-rotationportion 1220 of the bottom of a frame are shown in the example of FIG.12B.

Wiring Harness

After the battery blocks and inverter are mounted to the wall as part ofthe installation process, they are then electrically connected together.In some embodiments, a wiring harness such as that described above(where a segment of an external wiring harness is shown at 312 of FIG. 3) is used to connect the battery blocks and the inverter together,simplifying the wiring installation process.

FIG. 13 illustrates an embodiment of a power system. The following is anexample of a power system with an energy storage system with multiplebattery blocks stacked on top of each other. In some embodiments, powersystem 1300 is an example of power system 100 of FIG. 1 . In thisexample, a 20 kWh system is shown with 4 battery blocks (where eachbattery block is a 5 kWh subsystem). While an example battery systemwith four battery blocks is shown for illustrative purposes, the modularand scalable battery system may be configured to have any number ofbattery blocks, as appropriate. In this example, the battery system ismounted on the wall, without an aesthetic cover or shield shown.

A wiring harness is shown at 1302. In this example, the wiring harnesshas five connectors on it; one for each of the four battery blocks, andone connector that plugs into the inverter 1304 via plug 1306. In someembodiments, inverter 1304 is an example of inverter 102 of FIG. 1 .

As described above, each battery block has a DC-DC converter, which allfeed into the one central inverter 1304. The inverter is responsible forconverting between power from the battery, power from the solar panels,and power from the grid, and trading between them as needed by the powersystem.

In some embodiments, the battery blocks are individually connected tothe inverter, without daisy chaining or serialization. Here, in thisexample, the inverter sees four different battery block inputs. In thisway, power from the battery blocks may be controlled or treatedindividually by the inverter. Further, if a user has a system with fewerbatteries, either intentionally or by accident, the battery system canstill operate. For example, if one of the connectors was to becomeunplugged or one of the battery blocks was to go offline, the otherbattery blocks would still be able to work independently (without beingimpacted by the offline battery block). Additionally, if the batteryblocks were out of balance (e.g., one was less healthy than the otherthree), the weakness of one battery block does not limit theeffectiveness of the other battery blocks.

There are various benefits to the modular battery storage designdescribed herein. For example, there are various thermal benefits of thebattery block and battery module designs described herein. As describedabove, during normal thermal operation, air directly passes over theouter surface of a can or module. This in contrast to existing batterysystems, where the cans holding battery modules are typically furtherincluded in another sealed enclosure. Here, in this example, there isnot another enclosure into which the modules are placed. This providesvarious benefits. For example, additional enclosures need not be built.As another benefit, there is a reduction in the number of layers betweenthe heat of the cells to be removed and the ambient air. The batterymodule design and cooling described herein is more thermally efficient,as well as more mass cost-efficient, compared to existing batterysystems.

Further, using the cooling designs described herein, not only arethermal events and exhaust gases managed, environmental exposure is alsomanaged. This is unlike existing battery systems that employ internalcans to manage the safety cases described herein. Existing cans aretypically either not entirely sealed, or the cans themselves are proneto corrosion damage, thus requiring the need for yet another sealed box,which is not needed using the battery design described herein.

Improved ease of installation is also facilitated by the battery systemdesign described herein. For example, using the battery blocks describedherein, the installer simply takes the battery blocks, hangs them on thewall, and then plugs in the wiring harness to the battery blocks and theinverter. Further, installation safety is also improved, as theinstaller need only plug in the touch-safe wire harness connector.Further, an electrician need not be required for this portion ofconnecting battery blocks. For example, after an inverter has beeninstalled and wired into the building, the wiring harness can be easilyplugged in.

Described above are embodiments of a battery assembly (e.g., batteryblock). In some embodiments, the battery assembly includes a stack ofsubstantially planar modules. Each module has an inner set of batterypouches, a top insulator layer, and a bottom insulating layer. Eachmodule further includes a side region with thermally conductivematerial. Each module further has a thermally conductive shell. Thethermally conductive shell may be made of metal. The shell has a bottom,sides, front, rear, and top. In some embodiments, the front of the shellis the terminal side of the module that houses electrical connectionssuch as electrodes. Via the electrodes, the modules may be connectedtogether (e.g., serially) and their output provided to a DC-DC converterof the battery assembly, as described above. The rear of the shellincludes the venting side or heat exchanger side of the module, fromwhere gases are vented or exhausted out. In some embodiments, the shellis in communication with a blow-out valve. The blow out valve is incommunication with a common exhaust diffuser that is common to all ofthe modules. In some embodiments, the back blow-out valve is incommunication with a sealed passageway. The sealed passageway directsgas out of the valve to the exhaust diffuser.

In some embodiments, a thermally absorptive material is included on thetop of the shell of the module. In some embodiments, the thermallyabsorptive material includes phase change liquids such as liquids thatboil off or vaporize.

In some embodiments, the battery assembly includes a forced air systemthat causes air to flow along the sides of the module such that heat istransferred from the inner battery pouches to the outer sides to a heatexchanger. This cools the battery assembly during normal operation,where the shell of the module is in direct communication with theoutside ambient air. That is, the same thermally conductive shell thatseals the battery pouch cells is also thermally conductive to allow heatdissipation and transfer of heat away from the battery pouches. Further,exhaust gases are managed within the thermally conductive sealed shell(rather than having another outer shell to manage exhaust gases, as isthe case in existing battery systems in other applications such asautomotive and aircraft spaces). In some embodiments, the batteryassembly is covered by a vented shield.

Cell Temperature Regulation

Described above are embodiments of cooling the cells in the modules of abattery block using ambient air. As described above, for example, inconjunction with FIGS. 4B and 4C, a fan 404 is used to draw air from theright side of the battery block, across the sides of the battery modules(where the shells are thermally conductive), then over the heat sink towhich the power electronics (e.g., DC-DC power converter) are attached,and then out the left side of the battery block. In this way, theambient air drawn in by the fan is used to cool both the battery cellsand the electronics in a battery block.

In the cooling configuration described above, the fan is run in what isreferred to herein as the “forward” direction. In some embodiments, thefan is a bi-directional fan that may be run in both “forward” and“reverse” directions. As will be described in further detail below, theuse of such a bi-directional fan, along with the cell temperaturecontrol techniques described herein, allows for not only cooling ofbattery cells, but also heating of the battery cells, as well asmaintaining of the temperature of cells within a desired range. Forexample, the bi-directional fan may be run in different directions forvarious amounts of time at various speeds to achieve a desiredtemperature control goal or target.

The following are further details regarding cell thermal regulation.

Cell Heating

In some embodiments, heating of the cells in the battery modules isfacilitated by running the bi-directional fan 404 in reverse. Forexample, in the example of FIG. 4C, when the fan is run in the “forward”direction, ambient air is drawn from the right side of the batteryblock, where it passes along the channels of the battery module,absorbing heat from the battery cells, cooling them down. The air isthen driven past the heat sink to which the DC-DC power converter andother power electronics are attached, where the waste heat from theDC-DC power converter is transferred to the air (thereby cooling theDC-DC converter). The heated air is then pushed out the left side of thebattery block.

When the fan is run in the reverse direction, ambient air is drawn, bythe fan, from the left side of the battery block (where the opening onthe left side of the aesthetic cover is now the inlet, and the openingof the right side of the aesthetic cover is now an outlet). The ambientair is then heated by the waste heat generated by the DC-DC powerconverter. The heated air is then drawn in by the fan and pushed to theright, such that the heated air passes over the battery modules, therebycausing the cells to be heated.

In this example, the source of heat for heating up the drawn in ambientair is the waste heat of the DC-DC power converter. In otherembodiments, a battery block includes a dedicated heater for heating theair. The DC-DC power converter may be used standalone or in conjunctionwith the dedicated heater. That is, in various embodiments, the heatingenergy used to warm up the air being drawn by the fan may be from DC-DCwaste heat (e.g., based on the running of the DC-DC power converter, orby intentionally running the DC-DC power converter at low efficiency),fan waste heat, a designated heater, etc.

As another example, in some embodiments, the source of heat for warmingthe air being drawn across the cells may be a dedicated auxiliaryheating element such as a heating coil. In some embodiments, theauxiliary heating elements are placed in the battery pack. As anotherexample, a heat pump is used to heat the battery cells. The use of suchdedicated heaters as a primary heating source provides heating that maybe more efficient than relying on heat from control electronics to betransferred by air.

The following are examples of techniques for increasing the waste heatgenerated by the DC-DC power converter of the battery block. In someembodiments, the DC-DC power converter is run intentionally with lowefficiency (e.g., zero efficiency), thereby using the DC-DC powerconverter as a heater. For example, the DC-DC power converter isoperated to have a net throughput of zero. However, as current isflowing within the converter at high frequency, this creates loss (wasteheat) without pushing net power. This is inefficient from a power outputto waste heat standpoint, but is desirable in this heating scenario.

In some embodiments, the bi-directional fan need only be high efficiencyin the forward direction for cell cooling. In reverse mode,inefficiencies of the fan may help to promote heating. For example, whenusing the bi-directional fan for cell heating, lower fan efficiency isacceptable. In some embodiments, the DC-DC power converter and thebi-directional fan are intentionally run at low efficiency to generatewaste heat. In this case, a designated heater may not be needed. Forexample, if the fan were low efficiency when running in reverse, thenthe electricity will be turned to heat, contributing to the goal ofheating the battery cells.

Heating of the cells by running the bi-directional fan in the reversedirection may be performed for various reasons and to achieve variouscontrol targets.

Cold Start Heating

In some embodiments, running a bi-directional fan in the reversedirection is used to provide heating for cold start in cold weather. Insome embodiments, running the fan in reverse is the primary cell heatingtechnique for cold start in cold weather. In other embodiments, runningthe bi-directional fan in the reverse direction is used as a secondarycell heating technique that is used in conjunction with primary cellheating techniques such as heaters, heat pumps, thermoelectric heatingelements, etc.

Referring to the example of FIG. 4C, when the fan is run in reverseduring cold weather, cold air is drawn into the battery block by thefan, where the air is warmed by the heat from the DC-DC power converterand/or a dedicated heater, and then pushed over the battery cells,warming them, where the air then continues to the right and is exhaustedout of the battery block.

In this example of cold start, the ambient air is cold. In someembodiments, when the ambient air is cold, the fan speed is regulated tobe ultra-low. In this way, the air is passed through the battery blockslowly, such that the air loses the majority of its heat to the batterymodules before it drifts out of the other side of the battery block. Insome embodiments, the fan is run at ultra-low speed by pulsing the fan(e.g., causing the fan to rotate a quarter turn at a time). In thiscase, where the ambient air is cold, the DC-DC power converter willstill be cooled by the cold air, even if the fan is driving at a lowspeed (and the air flow/cubic feet per minute (CFM) over the powerconverter is low).

In other thermal states, such as where the ambient temperature is not ascold (and cold start of the energy storage system is not beingperformed), but the cells should still be heated, the fan may be run inreverse mode, but at a higher speed to allow for the DC-DC powerconverter to be cooled.

Although the energy usage efficiency may be low, it may be still moreoptimal than releasing all of the DC-DC waste heat to the ambient air,in which 100% of the DC-DC waste heat is wasted. Further, as compared torunning the fan in the forward mode, in which both the battery cells andthe DC-DC power converter are cooled, in the reverse mode, the DC-DCpower converter may still be cooled, while the battery cells are notsubjected directly to the cold ambient air, but instead to the airwarmed by the waste heat generated by the DC-DC power converter (thatis, there is an improvement as compared to running the fan in theforward direction, where the battery cells would be exposed to theunheated cold ambient air).

Cell Temperature Regulation

Described above are embodiments of using a bi-directional fan to supportheating and cooling of the battery cells/block. More generally, celltemperature control may be provided using the techniques describedherein. In some embodiments, and as will be described in further detailbelow, in addition to cooling and heating the battery cells, thebi-directional fan may be controlled in such a manner to maintain thetemperatures of the cells to be in a desired range.

That is, the bi-directional fan may be used for general cell temperaturecontrol. For example, during normal operation of the energy storagesystem, it may be beneficial to maintain the temperature of the batterycells in a desired temperature range (e.g., in an optimal temperaturerange for optimal cell performance). The bi-directional fan may be runseamlessly in both direction and flow rate to either cool or heat thecells, with forward, zero, and reverse air flow in order to achieve adesired air temperature. For example, the fan flow rate may be modulatedby changing fan RPM (revolutions per minute) in both directionscontinuously or stepwise, as desired. In addition, a desired airtemperature (before the air heats the cells) may be achieved byadjusting air heating power and air flow rate. As will be described infurther detail below in conjunction with FIG. 14 , the flow direction,flow rate, and air heater power may be controlled via a temperaturecontrol logic to allow the cells to operate in a healthy temperaturerange, where there may be different ranges for different goals (e.g.,safety, lifetime, power, capacity, SOC (state of charge) balancing,combined performance, etc.).

Maintaining a Desired Cell Temperature Range and Improving TemperatureUniformity

In some embodiments, during normal operation (or relatively lowertemperature operation), the fan direction and fan speed/velocity aremodulated intermittently or continuously (e.g., by sweeping between−10CFM to +10CFM). Such modulation of the fan allows the cell to operatein an optimal temperature zone with a small temperature variance acrossthe cells of a battery module (where such variance is also referred toherein as “delta-T” or “ΔT”). In some embodiments, the fan is operatedin a push-pull mode so that the overall pressure inside the batteryblock is maintained without lowering the overall pressure (and therebycausing outside air to be drawn in).

The ability to regulate/control the temperature of the battery cells tobe within a specified range of temperatures has various benefits. Forexample, the ΔT across the cells may be regulated to maintain the healthof the cells, improving their longevity. This may be achieved by runningthe fan back and forth (e.g., intermittently reversing the fanperiodically), which results in the delta-T of the cells being reduced.In this way, by having air flow in two directions, the temperaturegradient is reduced (as compared to one way air flow, which would resultin a temperature gradient from one end of a battery module to theother).

As another example of cell temperature regulation, rather than havingthe fan change directions back and forth, the battery block istransformed into a closed air loop system (further details of which aredescribed below) in which air is recirculated within the battery block,making the temperature of the battery block more uniform. In someembodiments, the fan velocity may also be modulated to facilitatecontrol targets such as maximum power density or power output.

Temperature Control Logic

As described above, by modulating fan parameters of a bi-directionalfan, such as RPM (revolutions per minute) and direction, the fan is ableto drive air in either direction, or switch air direction intermittentlyfor different purposes. In some embodiments, the fan is driven accordingto temperature control logic. In some embodiments, the temperaturecontrol logic is executed by a temperature control system. In someembodiments, the temperature control system is implemented in acomputing module, where the computing module may be a part of theinverter. In some embodiments, the temperature control system isconfigured to control the temperature at a battery block level, wherethe temperature of each battery block may be regulated independently ofthe other blocks. The temperature control system may also monitor eachbattery block individually and coordinate aggregate cooling of theenergy storage system by providing individual control of each batteryblock. The temperature control system may also control subsets of blocksof the energy storage system as a group, or determine an overalloperating mode of the heating/cooling systems of each block.

In some embodiments, the temperature control system may determine, for agiven block, the mode of operation for heating/cooling of the batteryblock, where the bi-directional fan is controlled in different ways fordifferent modes of operation. There may be various triggers fordetermining when to transition between different temperature regulationstates/modes. Further details regarding embodiments of logic for celltemperature control are described below.

FIG. 14 illustrates an embodiment of bi-directional fan control andlogic. In this example, there are three modes (states) of operation. Thetemperature control system may operate in other modes (states). In someembodiments, each mode further includes one or more sub-modes withdifferent conditions. The following are examples of temperatureregulation modes.

State 1 (1402). Forward fan direction (air flow) for cell cooling

State 2 (1404). Reverse fan direction (air flow) for cell warming

State 3 (1406). Oscillating fan direction (air flow) to, for example,reduce cell thermal gradient and improve cell temperature uniformity(delta T). This includes oscillating the fan back and forthintermittently, or continuously

In various embodiments, inputs and outputs of the control logic include:

-   -   Inputs        -   Monitored values—in various embodiments, the temperature            control system monitors:            -   ambient temperature            -   battery cell temperature field            -   DC-DC power converter temperature            -   battery states, such as state of charge (SOC), state of                health (SOC), state of power (SOP), and state of energy                (SOE). Battery states that are monitored may also                include electrical characteristics such as voltage,                resistance, etc.            -   ΔT: In some embodiments, the ΔT is the maximum                difference between any two points of the battery cell.                In some embodiments, ΔT is measured using temperature                sensors. In other embodiments, ΔT is predicted according                to a model.        -   Control targets (e.g., battery lifetime, maximum power            density, maximum performance, etc.)    -   Outputs In various embodiments, the temperature control system        modulates:        -   Fan control parameters such as fan direction and fan RPM. In            some embodiments, the temperature control system outputs            instructions to a fan controller for controlling the            operation of the fan. As one example, if the fan includes            stepper motors, where a set of switches are turned on and            off at the appropriate time to cause the fan to move a            certain way, then an appropriate control pattern may be            transmitted to the fan controller to control the direction            and speed of the fan. As another example, for a PWM            (pulse-width modulation) fan, the output may be a duty cycle            that is provided as input to a fan controller, where the fan            controller reads the duty cycle and operates the fan            accordingly        -   Closed/open loop parameters, such as the opening of baffles,            valves, dampers, etc., as will be described in further            detail below with respect to transforming a battery block            into an open air or closed air loop system.

The following are example triggers for switching between states,depending on system status and control targets:

-   -   1==>2: Energy System state/status: the ambient temperature is        below a low ambient temperature threshold. Control target:        Heating of the battery should be performed.    -   2==>1: Energy System state/status: the ambient temperature is        above a high ambient temperature threshold. Control target: The        battery should be cooled.    -   1==>3 and 2==>3: Energy System state/status: Temperature is        moderate, but cell thermal gradient (ΔT) is large. Control        Target: Temperature uniformity should be reduced using        oscillating air flow.    -   3==>1: Energy System state/status: The battery thermal gradient        (ΔT) is within limit, but cell should be cooled (control        target).    -   3==>2: Energy System state/status: Battery thermal gradient (ΔT)        is within limit, but cell should be heated (control target).

As shown in the above example logic, there are different controlalgorithms for different modes of operation.

The use of a bi-directional fan in conjunction with the temperaturecontrol logic described above has various benefits. For example,implementation complexity may be minimized, as there are minimalhardware, software, and firmware modifications to be made. Further,there is flexibility in the various modes of operation that are allowed.

In some embodiments, the output is controlled to balance the warming ofthe batteries with the cooling of the power electronics. For example,having low airflow may be beneficial to keep the batteries at a warmtemperature. However, this is less optimal for the DC-DC powerconverter, which may become hot and need to be cooled (e.g., forreliability purposes). In some embodiments, the temperature of the DC-DCconverter is also measured, where the amount of cooling needed may beused to determine the amount of airflow needed. As shown in the aboveexamples, in some embodiments, the direction of the fan may also bebased on the outside temperature and the cell temperature.

Closed Air Loop Configuration

In some embodiments, the battery block is implemented such that it canbe operated in an open air loop mode or a closed air loop mode. As willbe described in further detail below, ducts, dampers, valves, etc. maybe used to transform the battery block from an open air loop mode into aclosed air loop mode, and vice versa.

The ability to operate the energy storage system (and its batteryblocks) in a closed air loop has various benefits. For example, when inheating mode, heat is entrapped in the closed loop and the energy usageis much higher (e.g., ˜100%), as compared to the “air in & out approach”(e.g., open air mode) where much of the heat may be transferred to theambient air/environment. Also, the use of a closed air loop system maybe beneficial in situations where the DC-DC power converter should becooled, but the battery should be heated. In some embodiments, a coldbattery (with large thermal mass) may be used as a heat sink to coolDC-DC power electronics that are running hot.

The closed air loop system may be combined with a bi-directional fan tomodulate air flow direction and flow rate to help cells operate in adesired temperature zone/range or to achieve other temperature controltargets/goals. In some embodiments, the direction and speed of the fan,along with whether the battery block is in open air or closed air loopmode (e.g., by control of ducts, valves, dampers, flaps, etc.) iscontrolled by the temperature control logic described above.

FIGS. 15A-15C illustrate an embodiment of a system that may be operatedin either an open-loop mode or a closed-loop mode. In the examples ofFIGS. 15A-15C, the battery block includes recirculation ducts andopenings that may be opened/closed. This allows for both forward andreverse air flow (when open), as well as a circulation mode of operation(when closed). For example, the battery block includes ducting toconnect the outlet and inlet ports together. In the case ofrecirculation, rather than pulling air from outside, the fan acts as acirculation fan, averaging the temperature inside a battery block bycirculating air from the batteries to the electronics. A flap may alsobe used to close off the inlet/exhaust ports. Further details regardinga closed air loop mode for recirculation are described below inconjunction with FIG. 15C.

FIG. 15A illustrates an embodiment of an open-air loop operation modefor cooling. In this example, a top-down view of a battery block isshown, where the wall on which the block is mounted is at the backside.In this example, the battery block includes frontside recirculation duct1502, backside recirculation duct 1504, left opening 1506, and rightopening 1508.

In this example, the battery block is in an open air loop mode, whereopenings 1506 and 1508 are opened, and recirculation ducts 1502 and 1504are closed. In this example of cooling, the fan 1510 operates in the“forward” direction and drives air from right to left. When in thisforward direction, the cells are cooled, similar to as described inconjunction with FIG. 4C.

FIG. 15B illustrates an embodiment of an open-air loop operation modefor heating. In this example, the battery block is in an open air loopmode, where openings 1506 and 1508 are opened, and recirculation ducts1502 and 1504 are closed. In this example, the fan 1510 is run in the“reverse” direction, and drives air from left to right. As describedabove, when operating in this mode, the cells are heated using heat froma source such as DC-DC power converter waste heat and/or a specificheater.

FIG. 15C illustrates an embodiment of a closed-air loop operation mode.As shown in this example of a closed air loop mode, openings 1506 and1508 are closed, and recirculation ducts 1502 and 1504 are open. In thisway, by closing ports 1506 and 1508, any air flowing in the block doesnot exit out of the battery block, but is instead recirculated withinthe battery block. In this example, the fan 1510 pushes air from left toright. The fan is also able to push air from right to left. For example,the air flow in the circulation ducts 1502 and 1504 can be right-to-leftor left-to-right depending on the direction that the fan is being run.Thus, in the backside sub air loop (e.g., between the backside sidechannels and the backside recirculation duct) and the frontside sub airloop (e.g., between the frontside side channels and the frontsiderecirculation duct), the air flow may be clockwise or counter-clockwisedepending on fan direction. In some embodiments, in the closed-loop modeshown, air may be flowed continuously in one direction, or air flowdirection may be switched intermittently, for example, by changing fandirection. Switching air flow intermittently may be beneficial to aid incell temperature uniformity.

A recirculation duct may be implemented as a single duct or multiplesmaller ducts. In some embodiments, a recirculation duct is a separatepart, or is combined with a side channel (of the battery modules) as asingle part or component.

The valves/dampers for the recirculation duct (for opening or closingthe recirculation duct to allow air flow through the recirculation duct)may be placed anywhere along the recirculation duct. The valves/dampersmay be separate from the duct or integrated as a combined piece.

In some embodiments, the valves/damper openings are independentlycontrollable. This allows for improved control of air flow rate for thefront and back branches (which can facilitate achieving improved celltemperature uniformity for front cells versus backside cells, as thefront side and backside may have different thermal requirements).

FIGS. 16A-16B illustrate an alternative embodiment of a system that maybe operated in an open-loop mode or a closed-loop mode. In this example,the battery block uses the aesthetic cover as a recirculation duct wall.There is a single recirculation path in this example. A damper/valve isplaced in the recirculation path to open/close the recirculation path.

FIG. 16A illustrates an embodiment of an open-loop operation mode. Inthis example, (a) the aesthetic cover is used as a recirculation ductwall; (b) in this example, one recirculation path is shown at thefrontside; (c) in this example, a damper/value 1606 is inside thecirculation path and used to close or open the recirculation path. Thefan direction determines whether cell heating or cooling is beingperformed. In this example, the openings 1602 and 1604 are open, and thedamper 1606 is closed, closing the recirculation path. With this openair loop configuration, the cells may be warmed by running the fan 1608in in a direction such as to cause air to be driven from left to right.The cells may be cooled by running the fan 1608 in the oppositedirection (with air being driven from right to left).

FIG. 16B illustrates an embodiment of a closed-loop operation mode. Inthis example, the openings 1602 and 1604 are closed, and thedamper/valve 1606 is open (allowing the recirculation path/duct to beopen). This allows air to be recirculated within the battery block,making the temperature across the cells more uniform, and reducing thedelta T across the battery cells. The fan 1608 may be run in variousdirections (or run in an oscillating manner) to facilitate circulationof air within the battery block.

The following are further details regarding the temperature controlimplementations described above in conjunction with FIGS. 15A-15C and16A-16B. The use of a closed air loop system for cell heating hasvarious benefits, such as higher energy use efficiency than in the openair loop configuration.

In some embodiments, each recirculation duct can be one single duct ormultiple smaller ducts. In some embodiments, each recirculation duct maybe a standalone part, or combined with a side channel as a single part.

The valves/dampers for each recirculation duct may be put anywhere alongthe recirculation duct, where the valves/dampers need not be at theinlets or outlets. The valves/dampers may be linear or angular. Invarious embodiments, the valves/dampers are motor-driven (e.g., linearor rotary motion), passive (e.g., thermostat), or manually operated. Insome embodiments, with motor-driven valves/dampers, power-savingmeasures are implemented, where the motor-driven valves/dampers onlyconsume energy for switching states. For example, power-savingdampers/valves may be used that only consume energy during the openingor closing process, and that do not consume energy to maintain itsopened or closed state.

In some embodiments, the valve/damper opening for the front and backrecirculation path is independently controllable, as the cells at thefront side and the back side may have different thermal requirements(e.g., different ambient temperatures, wind speed, heat loss rate,etc.).

In some embodiments, each valve/damper is standalone. In otherembodiments, multiple valves/dampers may be combined as one integratedvalve/damper.

In some embodiments, the same dampers/valves in different blocks (thatare at the same location within each block) are connected together sothat they can be opened/closed simultaneously (e.g., controlled as agroup by the temperature control logic described above). In someembodiments, the individual valves/dampers within each battery block areconnected together so that they can be opened/closed together. In otherembodiments, each damper/valve is independently controllable.

As shown in the above examples, in some embodiments, the aesthetic coverserves as a recirculation duct wall (similar to the gas tank in anairplane wing, in which the wing skin serves as the gas tank wall).

In the above examples of FIGS. 15A-15C, the battery block includes tworecirculation ducts (both front side and back side). In otherembodiments, there is a single recirculation duct (e.g., as shown in theexample of FIG. 16B). In some embodiments, the space between batteryblocks may also be used as a recirculation duct passage.

In some embodiments, in an open air loop flow design (e.g., withoutrecirculation ducts), two dampers are included in the battery block, oneat the main inlet and one at the main outlet, to avoid cold air enteringthe battery block in cold and windy weather.

The closed-loop air flow battery block designs described above may beused in conjunction with a bi-directional fan as described above, or maybe used independently of each other.

Bus-bar heating

The following are additional embodiments of techniques for heatingbattery cells. As described above, in some embodiments, the batteryblock includes bus bars used to connect the various battery modulestogether. In one embodiment, the cells are heated by heating the busbarsconnected to the tabs on each battery cell, where heat is conductedthrough the tabs, directly into the cells. In some embodiments, thebattery cells are heated from one end. In other embodiments, in order toreduce the temperature gradient across the battery cells, the heating isperformed slowly. In another embodiment, the battery modules are adaptedto facilitate two sided heating. This reduces the delta T across thebattery cell.

As described above, the battery cell cooling/heating techniquesdescribed herein are implemented on a per-battery block level. That is,the temperature regulation of the battery blocks may be controlledindependently and separately from each other. In this way, thetemperature of each of the battery blocks may be controlledindividually, for example, with different flow rates. This providesvarious benefits, as the energy storage system is scalable and easy tocontrol at a granular level (where the heating/cooling is alsoscalable).

Although the foregoing embodiments have been described in some detailfor purposes of clarity of understanding, the invention is not limitedto the details provided. There are many alternative ways of implementingthe invention. The disclosed embodiments are illustrative and notrestrictive.

What is claimed is:
 1. An energy storage system, comprising: an energystorage component; heat generating electronics; and a fluid circulatorthat transfers fluid between the energy storage component and the heatgenerating electronics; wherein the fluid circulator is controlled toalternatively transfer fluid from a battery to the heat generatingelectronics or from the heat generating electronics to the energystorage component based at least in part on a thermal state of theenergy storage system.
 2. The energy storage system of claim 1, whereinthe energy storage system comprises a set of vents.
 3. The energystorage system of claim 1, wherein the energy storage system comprises aset of sensors, and wherein the thermal state of the energy storagesystem is determined based at least in part on measurements recorded byat least some of the set of sensors.
 4. The energy storage system ofclaim 1, wherein the heat generating electronics comprise a DC-DC powerconverter.
 5. The energy storage system of claim 4, wherein a throughputof the DC-DC power converter is controlled to generate waste heat. 6.The energy storage system of claim 1, comprising a plurality of modules,wherein a module comprises the energy storage component.
 7. The energystorage system of claim 1, wherein the heat generating electronicscomprise a primary and secondary heating element.
 8. The energy storagesystem of claim 1, wherein the fluid circulator comprises a fan.
 9. Theenergy storage system of claim 8, wherein the fan is bi-directional. 10.The energy storage system of claim 9, wherein a direction of the fan iscontrolled based at least in part on the thermal state of the energystorage system.
 11. The energy storage system of claim 9, wherein aspeed of the fan is controlled based at least in part on the thermalstate of the energy storage system.
 12. The energy storage system ofclaim 1, wherein the energy storage system comprises a valve, andwherein the valve is controlled to facilitate forming a closed air loop.13. The energy storage system of claim 1, wherein the fluid circulatoris controlled based at least in part on ambient air temperature.
 14. Theenergy storage system of claim 1, wherein the fluid circulator iscontrolled based at least in part on a variance in temperature across atleast a portion of the energy storage component.
 15. The energy storagesystem of claim 14, wherein the variance in temperature is determinedbased at least in part on temperature measurements taken at one or morepoints of the energy storage system.
 16. The energy storage system ofclaim 14, wherein the variance in temperature is predicted according toa thermal model.
 17. The energy storage system of claim 1, wherein thefluid circulator is controlled based at least in part on a temperatureof a DC-DC power converter.
 18. A method, comprising: controlling afluid circulator to alternatively transfer fluid from a battery to heatgenerating electronics or from the heat generating electronics to anenergy storage component based at least in part on a thermal state of anenergy storage system comprising the energy storage component, the heatgenerating electronics, and the fluid circulator.